# How much would 5 gigatons of methane warm the atmosphere compared to 5 gigatons of CO2 if both were released in one go?

I don't know much about science, I'm just curious about how much warming a certain amount of CH4 would cause compared to a similar amount of CO2 (both 5 GtC). I'm sorry if the question sounded a bit confusing, I'm just a layman trying to learn more about global warming and climate change.

• Please revise your post to ask one question and state what research you have done and any supporting material you think is relevant. Also you should be specific about the present and future conditions you are assuming. Do you mean how much would it warm the atmosphere under current conditions? If so, would other emissions stay the same over the next 100 years? Warming potential won't be the same for all climate regimes or scenarios.
– f.thorpe
Jul 23, 2021 at 17:26
• Is this question essentially a duplicate of your unanswered question from a few weeks ago: earthscience.stackexchange.com/questions/22386? It's 5 GtC rather than 50 GtC, but it feels like you're still interested in that kind of information. Jul 24, 2021 at 11:15
• What you are asking would require several assumptions. Converting from an emission rate to a well-mixed global concentration is not trivial. I think you would generate more interest if you asked in terms of global concentrations in a well mixed atmosphere. For instance, methane is currently at 2 ppm and CO2 is at 400 ppm. You could ask about a different mixing ratio scenario.
– f.thorpe
Jul 25, 2021 at 4:25
• @Victor1995 Please show your work. You should be able to do a back-of-the-envelope calculation with information readily available online. From what I can find, in 1951 the CO2 content of earth's atmosphere was about 310ppm, but by 2012 this had increased to about 400ppm. The ppm values correspond to 660 GtC (2430 GtCO2) for 1951 and 853 GtC (3130 GtCO2) for 2012. Over this time, global temperature increased by 0.12 degC per decade on average. Most but not all of the temperature increase was from CO2, but for simplicity (and additionally neglecting hysteresis effects) you could assume it was. Jul 25, 2021 at 5:41
• @Victor1995 Relevant online resource: On the causal structure between CO2 and global temperature Jul 25, 2021 at 5:42

In theory, the methane emissions would warm the earth about 25 times more than the carbon dioxide emissions.

That's because of something called the global warming potential. The global warming potential of a greenhouse gas is how much it warms the planet compared to carbon dioxide's base value of 1. As you might expect, methane's GWP is 25.

• Global Warming Potential is time based. The value of 25 (range 21 to 40) only applies to period of 100 years. For a 20 year period the range of GWP values is 56 to 96 & for 500 years the range is 6.5 to 7.6.
– Fred
Aug 30, 2021 at 8:52
• Yeah sorry I should have mentioned that; Victor mentioned he was just trying to understand so I was ttrying to keep it simple. Aug 30, 2021 at 13:28

Figure 3a of Evaluating Climate Emulation: Fundamental Impulse Testing of Simple Climate Models compares the temperature response of pulses of CO2 and HC4 (I can't see where they specify the relative quantities).

• This impulse response seems to contradict the relative strength of methane to CO2 warming as is usually quoted... the effect from Methane here seems much weaker than 25-40 times larger, what am I missing? Nov 18, 2021 at 16:55
• @AtmosphericPrisonEscape As I say, I can't find the quantities in that paper. The curves on the first graph here seem to be equivalent GWP, so if it was equivalent mass, the CH4 curve would be 25 times higher? Nov 18, 2021 at 19:13
• Yes, it should be higher by that factor, if no other effects interfere. I did a quick computation of the Rosseland optical depths of H2O+CO2 vs. H2O+CH4 (for the same amount of mass released each) and the resulting temperature difference in a radiative steady-state is 1.1K vs. 40K, so that seems to be this famous factor 40. Guess I could post this as an answer, if someone thinks it would be useful. Nov 18, 2021 at 20:18